Eds, I use lime juice and lemon juice in chlorinated water and it does a reasonably good job (both lemons and limes being high in citric acid). I have never used citric acid in sachets so am not sure how effective it would be, but it would be worth giving it a try.
I don't know what the current one of choice for the forces is, but on water points they used to use Calcium Hypochlorite to treat the water through a variable volume doser, once the chlorination had been stabilised at the correct level and correct soak times had been observed the water would then be decanted of into water bowsers where they would have sodium thiosulphate added to them. This both speeded up the removal of the Hypochlorite and had a detaste effect.
It's pretty pokey stuff though, you're looking at 0.1 and 0.3 gramms of crystalline thiosulphate to ten litres of tap water.
Swimming pools are dosed at a rate of 0.4ppm - 1.4ppm of chlorine (that's according to WHO). Sometimes they shock dose a pool to get rid of problems at a rate of 20ppm, when they do that they use thiosulphate to reduce the chlorination levels to an acceptable level in a shorter period of time.
The water that goes through a water point used to be dosed at 5ppm, left for a soak period and then retested, it had to achieve a minimum of 2ppm (so stronger than your average swimming pool). When dosed with thiosulphate it was drinkable within the hour with a very slight chlorinated taste (a lot less than we seem to be getting from the taps here in the mornings anyway
).